Sorbent type filter assemblies for respirators are well known in the art. The filter assemblies customarily have a sorbent bed formed from a granular material which could be, for example, activated charcoal. In order to prevent the sorbent bed from shifting during use, which shifting could lead to early breakthrough of noxious gases, it is customary to maintain the sorbent bed under compression. In a typical application this is achieved by providing a spring which is biased against a perforated plate or screen to hold the perforated plate or screen against a retention filter which is in turn biased into contact with the sorbent bed on one side, the other side of the sorbent bed also being retained by a retention filter and perforated plate or screen.
Sorbent bed filters may also be associated with particulate filters for filtering out airborne particles.